In tracking systems that include many portable, tracked remote units it is important coordinate the handoff between different monitors as the portable, tracked remote units move about and lose contact with one or another monitor. This problem is especially severe when communication requires line-of-sight (LOS) transmission of signals. In such systems, it is additionally desirable or essential to be able to assure that a message from a remote unit will be acknowledged by the monitoring sites in an organized fashion that assures reception of the acknowledgment by the remote unit that sent the initial message. This is particularly critical when the message that is being sent by the remote unit is an emergency (911) call which additionally provides descriptive information through a selectable canned message library or though a character-limited text message.
Thus, what is needed is a practical, economical method for providing seamless handoff between a multiplicity of monitors that are monitoring a (typically larger) number of remote units via a time division multiple access (TDMA) communications linkage. In such a system, it is particularly important to provide an acknowledging signal in an orderly fashion, especially when the initial communication is urgent.